It is known to measure the thickness of a strip or metal sheet exiting from a rolling pass by detecting the absorption of a bundle of ionizing radiations, for example X rays, emitted by a source and striking, advantageously perpendicularly, a surface of the sheet. A part of the bundle of rays is attenuated since it is absorbed both according to the type of material which makes up the sheet, and also according to the thickness that the bundle of rays passes through. The component of the bundle that passes through the sheet is measured by a receiver element disposed on the opposite side with respect to the source of the bundle, thus allowing to measure the thickness.
To ensure both adequate accuracy and repeatability of the measurements of thickness, it is necessary for the emission to be kept stable, for example by keeping the emission source at a constant or controlled temperature.
Known cooling devices, for example with the circulation of cooling fluid, in contact with the walls of the emission tube, are not always effective, they require complex systems to feed, circulate and discharge the fluid and are costly to install and maintain. Consequently, it is not always possible to guarantee accurate measurements in all working conditions.
One purpose of the present invention is to achieve a thickness measurer for metal sheet or strip and the relative measuring method, which allow to carry out the measurements with the desired accuracy and repeatability even when the working conditions vary.
Another purpose of the present invention is to achieve a thickness measurer which allows to reduce the cost of the measurer and also the costs of management and maintenance.
The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.